Fix potential infinite loop in ClassUtil (internalMethodParameterCount)

[hsuk04]

Description

Applying a fix that was applied to the original codebase https://github.com/Guardsquare/proguard-core/commit/c6d8746b06d8ab8bff55b6609eb700f2387778eb that has not been applied here yet.

As per the original commit: Summary: When you forget an ending semicolon in a method descriptor, e.g. (Ljava/lang/String)V, the parameter count method previously just ended up in an infinite loop. This is now detected and prevented by throwing an exception.